Since the electroluminescence of poly(p-phenylene vinylene) (PPV) was first reported by Burroughs et al, Cambridge Univ. U.K. in 1990, the polymeric electroluminescent material and manufacturing device thereof has been extensively concerned and investigated by the research and industry circles due to its prominent characteristics of simple process, easy to achieve large screen display and flexible display etc. At present, some typical blue-, green- and red-light polymeric luminescent material systems, such as poly(p-phenylene) (PPP), poly(alkylfluorene) (PAF), poly(phenylvinylene) (PPV), polythiophene (PTh) etc, have been developed. All the performance indexes of the monochromatic light polymeric electroluminescent device made of them can fulfill practical requirements. By contrast, there is a larger gap between every performance index of white light polymeric device and practical requirement. It is necessary to research deeply the material design and device structure separately so as to accelerate the course of industrialization of white light polymeric device.
The means for achieving white light polymeric electroluminescent device mainly include: (1) blending system of organic fluorescent dye/polymer; (2) blending system of polymer/polymer; (3) single white light polymeric system. For example, J. kido et al. disclosed a method for obtaining white luminescence with a maximum luminance of 3400 cd/m2 by dispersing three kinds of fluorescent dyes (red, green and blue) in poly(vinylcarbazol) (PVK) and regulating the contents of the three dyes, Appl. Phys. Lett., 64, 815, 1994; Inganas et al. disclosed another method for obtaining a white light emission (CIE 0.220, 0.466) by blending the polythiophene derivatives (red, green and blue) with an inert polymer (such as PMMA) under a high driving voltage (20V), Appl. Phys. Lett., 68, 147, 1996. But the system has the following disadvantages: the obvious phase separation between polymer and polymer results in the voltage-dependence of white light emission, and thus a stable white light device is difficult to be obtained. Leising research group disclosed a method for obtaining a white light polymeric device having an external quantum efficiency of 1.2% by dispersing a trace amount (0.66 wt %) of red light poly(perylene-co-diethynylbenzene) (PPDB) in a high efficiency blue light laddertype (polyparaphenylene) (m-LPPP), in which the voltage-dependence of white color purity was improved to a certain extent due to the formation of a homogeneous blending system of polymer/polymer, see Appl. Phys. Lett., 71, 2883, 1997. For the single polymeric white light system disclosed in “Appl. Phys. Lett., 79, 308, 2001” and “Macromolecules, 35, 6782, 2002”, it is obtained by forming an exciplex during the electroluminescence of PPV polymer (blue or blue-green), which can bring about a wide-band luminescence, so the white light polymeric device made thereof has a sharp voltage-dependence of color and relatively poor performances.